System and method for controlling the operations of a manufacturing facility

ABSTRACT

A system and a method for controlling the operations of a manufacturing facility with production resources that execute a production process and a manufacturing execution system with a production modeler and a production scheduler. A man-machine interface and/or graphical user interface enable the user to enter production orders and production scheduling data into the execution system. A production scheduler database stores production orders and production scheduling data. A data server process updates sensitive data that are required for real-time scheduling when a user modifies sensitive data. The data server process executes an event list queue with the data modification events launched by the database, periodically checks the event list queue for data modification events, reads from the database only the modified data of the sensitive data and/or sensitive class of data, and merges the modified data with the existing data. The updated data are then accessible to all users.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of Europeanpatent application EP 11 183 718.3, filed Oct. 3, 2011; the priorapplication is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a system and a method for controllingthe operations of a manufacturing facility.

The present invention belongs to the field of modern manufacturingprocesses. Those manufacturing processes are highly automated and may bedivided into several hierarchical layers. For example, at the highestlevel, the enterprise resource planning (ERP) takes place, which may bereferred to as a business layer. At lower levels, the hardwareimplementation and control take place, which may be referred to asvarious control levels. Industry standard ISA S95 defines anintermediate layer that integrates and connects together business andcontrol layers. That intermediate layer is referred to as manufacturingexecution system (MES) that defines an MES process in terms of data andinteractions between functions, such as production modeling, productionscheduling, resource management, resource allocation, dispatching, datacollection and acquisition, quality assurance management, maintenancemanagement, performance analysis, corrective scheduling, documentcontrol, labor management and material and production tracking.

In the area of manufacturing execution systems, an extensive line ofproducts, such as, for instance, the SIMATIC® IT product from SiemensAG, Germany, is available for solving a variety of technical tasks. Inthis context, a broad range of IT solutions exist to connect the actualhardware close to the technical and/or logistical process to theapplication layer of the client driving the installation. Manufacturingexecution systems have therefore been developed to meet all of therequirements of a service-oriented architecture (SOA) to integrateseamlessly into a totally integrated automation (TIA). For example,SIMATIC® IT is the manufacturing execution system in TIA, and SIMATIC®PCS 7 is a process control system suitable for cooperation with amanufacturing execution system.

Commonly assigned U.S. Pat. No. 7,657,404 B2 (published US 2005/0159932A1) represents the various levels of a manufacturing process in form ofa pyramid. In that representation, the uppermost level is the ERP level,and the lowermost level of the pyramid is the automation/control level,wherein the MES level is the linking level. Programmable logiccontrollers (PLCs) in conjunction with visualization and process controlsystems (PCSs) are typically used on the automation level. Individualdrives, actuators and sensors used in the production and/ormanufacturing facilities are in direct contact with the systems of theautomation level.

U.S. Pat. No. 7,657,404 B2 (US 2005/0159932 A1) explains further that anMES system contains a runtime system (RTS) for providing time-basedsequence control of the components involved (sub-components, modules,tasks, operating system processes etc.), and an engineering system (ES)for creating and editing programs which are intended for execution inthe runtime system. A connection between the runtime system of thecontrol facility (or of the automation system or the MES system) and atechnical process is effected by way of inputs/outputs. The programmingof the control facility and with it the specification of the behavior ofthe runtime system is carried out in the engineering system. Theengineering system contains tools for configuring, planning andprogramming machines and controlling technical processes. The programscreated in the engineering system are transferred to the runtime systemRTS of a target system.

The control programs or installation specifications created by theengineering system are executed on a target system, for example, tocontrol a technical process. The target system includes processors,storage facilities and a runtime system. The ES-created control programsare loaded onto the target system's runtime system. The underlyingtechnical process, e.g., for an MES solution, is controlled via inputsand outputs. Actuators are influenced by the runtime system via theinputs and outputs. The technical process reacts by sending sensor databack to the runtime system via the inputs and outputs for furtherprocessing in the application.

Elements used for an installation description, or for a manufacturing orassembly solution (installation parts, installation components,machines, valves etc.) are linked in the engineering phase with metainformation or physically contain meta information in the productionmodel. Meta information may be information about the elements themselves(e.g., Who is using an element?, With which other elements does itinteract?, With which other elements it cannot interact in parallel?).However, meta information can also comprise knowledge about anapplication, the business process to be implemented or the entireinstallation. This type of knowledge is present in the engineering phase(in functional specifications, design specifications or otherinstallation documentation) and simply needs to be incorporated into theelements as meta information. In particular, the markup language XML(Extensible Markup Language) is suitable for describing meta informationand linking it with elements.

Further, the client needs to implement its own software programs andapplication for which the SIMATIC® IT offers a Client ApplicationBuilder (CAB) tool that enables the user to customize the SIMATIC® ITsoftware. All other MES software solutions probably will also comprise auser interface allowing the user the customization of thestandard-related MES software. In this specific context in particularand in general, a vast kind of data interactions and data handlingroutine are managed by web applications being incorporated by the CABtool into the MES software.

For the execution of the manufacturing process, it is thereforenecessary to have a production plan to manage all the processes of themanufacturing facility (factory). The user requests on production ordersare used to prepare a master production scheduler (MPS) using the MESproduction scheduler component. The MPS is the plan for production,staffing, inventory etc. and indicates when and how much of each productis required. The MPS quantifies significant processes, parts and otherresources in order to optimize the production process, to identifybottlenecks and to anticipate the needs and the completed goods. Sincethe MPS drives much of the factory's activities, its accuracy andviability dramatically affects the profitability of the plant. After theMPS the production orders need to be assigned and executed to thevarious lines and units of equipment in the plant to realize the MPS.This phase, which is called detailed scheduling, is the phase to whichthe present invention is related. The purpose of the detailed schedulingin an industrial scenario is to minimize the production time and costs.It has also a component in environmental protection when naturalresources, such as water and electric power, are managed to their best.The detailed scheduling tells the production facility what to produce,when, with which staff and on which equipment.

During detailed scheduling, the user (scheduler/planner) loads all thedata required to prepare the schedule plan (e.g. displayed in form of aGantt chart) in the production scheduler environment of themanufacturing execution system. When the user modifies the productionorder plan to optimize the scheduling, it may happen that another usermodifies simultaneously its schedule. This runs the risk that themodification made by the second user invalidates the schedule planned bythe first user. We shall explain by way of a few examples:

a) A first user prepares his schedule plan. A second user schedulesproduction orders that produce material used by the production ordersmanaged by the first user as input material. In case the second usermodifies his schedule plan, the schedule plan of the first user mightbecome infeasible, and the first user has to modify his schedule plan assoon as possible to avoid problems in the production.

b) A production order in production requires a halt due to adisturbance/failure of the respective production line; all users need tobe notified as soon as possible and review this situation immediately inorder to modify their schedule plan depending on the gravity of thedisturbance.

c) New production orders have been created in the system due to newurgent customer requests; all users need to review these new productionorders immediately to adapt/modify their schedule plan.

Presently, manufacturing execution systems (MES) manage this problem ofnotifying and updating the schedule plans by applications that use anautomatic process which periodically retrieves all therelevant/sensitive data from the database of the MES and brings the datato the attention of the users, such as displaying the data at a MMI/GUI,SMS-messaging and the like. Unfortunately, this process has a rather lowperformance because in many cases the data did not change but istransmitted anyway thereby occupying band width in the communicationbackbone of the MES. On the other hand, if a distinct production orderhas been modified by one of the user, all other user need to be informedabout this modification and not only about the recent changes. In otherapproaches, the update operation is done entirely manually by thecontrol user with the substantial drawback of being prone to delay,faults and low capacity.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a system and amethod for controlling the operations of a manufacturing facility, whichovercomes the above-mentioned disadvantages of the heretofore-knowndevices and methods of this general type and which offers a high levelof flexibility in scheduling the production processes and simultaneouslyrequire only a limited amount of bandwidth to manage the transfer of thedata that is relevant for real-time based scheduling.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a system for controlling the operationsof a manufacturing facility, the system comprising:

a plurality of production resources configured to execute a productionprocess according to a production schedule;

a manufacturing execution system comprised of, at engineering level, aproduction modeler configured to model the production resources andproduction dependencies and/or constraints thereof, and a productionscheduler configured to schedule the production process according toproduction orders to be executed thereby using a data model of theproduction modeler;

at least one man machine interface and/or graphical user interfaceenabling a user to enter production orders and/or production schedulingdata into the manufacturing execution system and to present all datarecords being relevant for the user when scheduling the productionprocess in order to have the user's production order scheduled andexecuted accordingly;

a production scheduler database configured to store all productionorders and/or production scheduling data and to provide predefined datastored in the database to the man machine interface and/or graphicaluser interface for the user in charge of scheduling; wherein thepredefined data are determined sensitive data and/or sensitive class ofdata out of the data stored in the database, the sensitive data and/orsensitive class of data being required for a real-time scheduling;

a data server process configured to update the sensitive data and/orsensitive class of data for the users when a user modifies at least partof the sensitive data and/or sensitive class of data; wherein said dataserver process is enabled to execute an event list queue formed of thedata modification events launched by the database, and said data serverprocess is further configured to:

i) periodically check the event list queue for data modification eventscovering the sensitive data and/or sensitive class of data,

ii) read from the database only the modified data of the sensitive dataand/or the sensitive class of data, and

iii) merge the modified data with the existing data wherein the updateddata are accessible by all users.

With respect to the method, the object of the invention is achieved by amethod for controlling the operations of a manufacturing facility,wherein the method comprises the following steps:

a) providing a number of production resources that execute a productionprocess according to a production schedule;

b) providing a manufacturing execution system comprising at engineeringlevel a production modeler to model the production resources and theirproduction dependencies and/or constraints and a production scheduler toschedule the production process according to the production orders to beexecuted thereby using the data model of the production modeler;

c) providing at least one man machine interface and/or graphical userinterface enabling the user to enter production orders and/or productionscheduling data into the manufacturing execution system and to displayall data being relevant for the user when scheduling the productionprocess in order to get his production order scheduled and executedaccordingly;

d) providing a production scheduler database that stores all productionorders and/or production scheduling data and provides predefined datastored in the database to the man machine interface and/or graphicaluser interface for the user in charge of scheduling; wherein thepredefined data is determined sensitive data and/or sensitive class ofdata out of the data stored in the database; said sensitive data and/orsensitive class of data being required for a real-time scheduling;

e) providing a data server process that updates the sensitive dataand/or sensitive class of data for the users when a user modified atleast part of the sensitive data and/or sensitive class of data; whereinthe data server process is enabled to execute an event list queue; saidevent list queue comprising the data modification events launched by thedatabase. The data server process is further enabled to:

i) periodically check the event list queue for data modification eventscovering the sensitive data and/or sensitive class of data,

ii) read from the database only the modified data of the sensitive dataand/or the sensitive class of data, and

iii) merge the modified data with the existing data wherein the updateddata is accessible by all users.

The system and method therefore have the main advantage that all userscan view always updated data and the respective application reads theupdates only when it is strictly necessary, thereby additionally limitedthose updates to the portion that have been changed since the last andthat belong to the predefined sensitive data. This measure tremendeouslyminimizes the data exchange in the production modeler and productionscheduler thereby reducing the bandwidth consumed and increasing theperformance of the overall manufacturing execution system whencontrolling the production accordingly. Therefore, also the robustnessof the planning and scheduling module increases because all users incharge with scheduling are always confronted with updated (most recent)real-time data.

In order to satisfy the demand on the real-time update, the system andthe method advantageously provide a data entry which enables a masteruser to define the period for checking the event list queue. Typicaltime periods for checking are under the consideration of the delay timein a factory in range of a few seconds up to maximum a few minutes.

Sensitive data and/or sensitive class of data are in the context of thepresent invention for example all data related to the usage of aresource, to the amount of material on stock, to the amount of materialto be delivered or produced, to the time intervals where resources aremaintained or for other reasons not productive and the like.

The method and the system can be in a preferred example of the presentinvention implemented in the form of a SQL Server Notification Servicethat allows to an user application to be notified when observed data hasbeen modified on the database. Notification Services provide aneasy-to-use programming model for generating and formattingnotifications based on personal subscriptions that are reflected in theEvent List Queue accordingly. Using the Microsoft ADO API, it is forexample possible to define an event to infer when the observed sensitivedata and/or sensitive class of data have been changed on the database.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a system and a method for controlling the operations of amanufacturing facility, it is nevertheless not intended to be limited tothe details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 a schematic illustration of one embodiment of a manufacturingexecution system in the environment of a production plant, and

FIG. 2 a representation of the substantial workflow of a method forcontrolling the operation in a production plant.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is illustrated a schematicoverview of a plant control system 2 working as a manufacturingexecution system (MES). The system/network 2 comprises a number of dataprocessing units 4, 6, 8, 10 running an MES software for controllingand/or monitoring a production process operating a number of productioncomponents 12 to 24. The production components 12 to 24 can be sensors,actuators, motors, step drives, conveyors, valves, pumps, completeunits, and the like. The data processing units 4 to 10 are networkcomputers which typically comprise logical units, calculation means,storage means, display means (man-machine interface MMI and/or graphicaluser interface GUI) and the like. The data processing units 4 to 10 areconnected within a plant network in order to exchange data to therequired extent. Usually, this connection is achieved by a W-LAN orcable-bound or mixed Ethernet connections. One of the data processingunits, hereinafter referred to a master console 4, is executing the MESsoftware for controlling and monitoring the operation of the plant.

The master console 4 comprises within the MES software a productionmodeler PM and a production scheduler PS. This production modeler PM isenabled to define a business logic BL within a fully graphicalenvironment as facilitated by the MES software. The business logic BL,when finally generated by the production modeler, comprises a plantmodel of the production process and the related operating procedures forthe production components 12 to 24 in a fully graphical environment.Even for the creation of the business logic BL high-level graphicallanguage is used within the MES software, preferably consistently withthe ISA-95 standard.

The master console 4 further comprises the production scheduler PS whichenables the user to define a workflow of production processes on theresources 12 to 24 and their dependencies and/or constrains as theresources have been modeled in the production modeler PM. The productionscheduler PS usually also displays the course of production operationson the display of one or more of the data processing units 4 to 10. Thedata displayed is usually prepared to fit into a real-time Gantt chartwhich shows the substantial operations and the usage of the resources 12to 24 in the past, at present and also in the future.

The master console 4 further comprises a client application builder CABwithin the MES software being enabled to provide a native, WEB basedgraphical user interface for various purposes. One purpose is ofgenerating cross-functionality graphic screens S, said screens formingpart of the network 2 as presentation clients PC, PC1 to PC4 anddisplaying data D which is stemming from the production components 12 to24 and which is manipulated from the business logic BL by the productionmodeler PM, where it is required, i.e. when the data stemming from oneof the production components 12 to 24 has to further processed oraveraged with data stemming from other production components. Ingeneral, the client application builder CAB within the Simatic IT®software suite provides a CAB Engineering module that offers a VisualStudio .NET environment where the CAB applications are developed by theuser. Further, the client application builder CAB comprises a CAB WebServer where CAB applications (those developed with the CAB Engineeringenvironment) are executed upon request of a user. Furthermore, the CABserver comprised in the client application builder takes care forexchanging data with the various SIMATIC IT® data sources and with theclient side. And last but not least the client application builder CABcomprises a CAB client which requires, by means of a Web browser,typically a resource (for example, the display of a set of data) to theCAB Web Server. On the CAB Web Server, two web applications areinstalled, on the one hand the SIMATIC IT® portal and the SIMATIC IT®console. These two applications allow the use and visualization of thecomponents also involved in the SIMATIC IT® software suite, such as theproduction modeler, production scheduler, production tracer and so on.

Using the man machine interface and/or graphical user interface of thedata processing means 4 to 10 the user is enabled to enter productionorders and/or production scheduling data into the manufacturingexecution system MES and to receive usually in a displayed form all databeing relevant for the user when scheduling the production process inorder to get his production order scheduled and executed accordingly. Aproduction scheduler database DB stores all production orders and/orproduction scheduling data and provides predefined data stored in thedatabase to the man machine interface and/or graphical user interfacefor the user in charge of scheduling. Thereby, the user is furtherenabled to customize insofar the predefined data as to determinesensitive data and/or sensitive class of data out of the data stored inthe database DB.

Sensitive data and/or sensitive class of data are in the context of thepresent invention for example is all data related to the usage of aresource, to the amount of material in stock, to the amount of materialto be delivered or produced, to the time intervals where resources aremaintained or for other reasons not productive and the like. Sensitivedata and/or sensitive class of data are essential for a real-timescheduling in order to be notified of the schedule decisions other userhave entered into the production scheduler.

The master console 4 is further linked to a data server process SP thatupdates the sensitive data and/or sensitive class of data for the userswhen a user modified at least part of the sensitive data and/orsensitive class of data. The data server process SP is enabled toexecute an event list queue ELQ; said event list queue ELQ comprisingthe data modification events launched by the database DB. The dataserver process SP is operated in order to:

i) periodically check the event list queue EQL for data modificationevents covering the sensitive data and/or sensitive class of data,

ii) read from the database DB only the modified data of the sensitivedata and/or the sensitive class of data, and

iii) merge the modified data with the existing data wherein the updateddata is accessible by all users of the production scheduler PS.

FIG. 2 illustrates the major steps in the workflow according to thepresent invention when controlling the production operations of theproduction plant 2. When a user start the production scheduler(application) SP on his personal computer PC1 to PC4 or on one of thedata processing means 4 to 10, the application loads all useful datafrom the database DB (at least the sensitive data and/or all sensitiveclasses of data) wherein for the sensitive data and/or the sensitiveclasses of data an SQL Dependency (SqlDependency) is activated toreceive the relevant data change events originated by the server processSP, i.e. a SQL Server Process.

To avoid that for every change of a single data entry all data displayedto the user in charge of scheduling is always refreshed, all the updatesof data notified from the database to the event list queue ELQ of theserver process SP, wherein the data needs to be comprised among thesensitive data and/or sensitive class of data, are collected and addedin the dedicated event list queue ELQ. Periodically at a time intervalspecified, the event list queue ELQ is checked, and if there are updateson the sensitive part of data found, the data initially read is updatedwith the values stored in the database and being present in the observed(sensitive) table with the recently modified data stemming from the lastupdate to the current update. To avoid any mismatch in the time rankingthe data has been amended, a time stamp column is provided in the tablesof the sensitive data and/or sensitive class of data. The productionscheduler application is in charge of updating this time stamp columnvalue every time the record changes by updating the time stamp, too. Thetime stamp itself usually has to be stored with a precision ofmilliseconds.

This way safeguards that the data displayed to the user in charge ofscheduling is always correct and reflect the scheduling process inreal-time. Any update operations are securely limited to those eventswhere changes in the sensitive data and/or the sensitive class of dataare found in the event list queue ELQ. Even in case that many dataentries have been changed in short term, the update can be executed byjust one read operation from the database DB. The flowchart shown inFIG. 2 illustrates the primarily important steps of the presentprocedure according to the present invention.

In step S1, an arbitrary user modifies its scheduled production orders.In step S2, this user entry is stored in the production schedulerdatabase DB. In step S3, the production scheduler database DB notifiesthe data server process SP that data has been changed by a user. In stepS4, the data server process SP receives a notification of the datachange event launched by the production scheduler database DB. Thesenotifications are stored into the event list queue ELQ. In step S5, theproduction scheduler application periodically checks the event listqueue ELQ and reads from the database DB only theinserted/modified/deleted rows of data that are assigned to thesensitive data and/or sensitive class of data. The data read issubsequently merged with the existing and unamended data in order togenerate a complete data record, ready to be conveyed to the user incharge of the scheduling. In step S6, the updated data record is shownto all associated users and the production process is currentlycontinued to the scheduled operation according to the latest confirmedproduction schedule. Due the possible amendments of the data, every useris in real-time mode enabled to reflect the consequences of the recentamendments on his individual scheduled production operations.

The system and method explained above therefore have the main advantagethat all users can view always updated data and the respectiveproduction scheduler application reads the updates only when it isstrictly necessary, thereby additionally limited those updates to theportion that have been changed since the last and that belong to thepredefined sensitive data. This measure tremendously minimizes the dataexchange in the production modeler and production scheduler therebyreducing the bandwidth consumed and increasing the performance of theoverall manufacturing execution system when controlling the productionaccordingly. Therefore, also the robustness of the planning andscheduling module increases because all user in charge with schedulingare always confronted with updated (most recent) real-time data.

A solution of the present invention has been based on the SIMATIC® ITProduction Suite database where only the production order and productionorder entries database are considered. The production schedulerapplication loads this data and displays this data to the users in twotables. The advantage of the present invention becomes apparent from asimple example. A scenario is considered where a user loads from theproduction scheduler database 16.000 production orders. The productionscheduler application reads all the production orders from theproduction scheduler database DB in about 300 ms wherein this time spanonly reflects the time for loading the data from the data base DB).Another user now modifies about 200 existing production orders (out ofthe amount of presently 16,000 pending production orders. The productionscheduler application loads after checking the event list queue on the200 modified production orders that requires about 30 ms which is tentimes less than the time required for loading the complete data set ofall existing production orders. This simple example easily demonstratesthe increase of performance that is achieved by the present invention.

The invention claimed is:
 1. A system for controlling the operations ofa manufacturing facility, the system comprising: a) a plurality ofproduction resources configured to execute a production processaccording to a production schedule; b) a manufacturing execution systemcomprised of, at engineering level, a production modeler configured tomodel the production resources and production dependencies and/orconstraints thereof, and a production scheduler configured to schedulethe production process according to production orders to be executedthereby using a data model of the production modeler; c) at least oneman machine interface and/or graphical user interface enabling a user toenter production orders and/or production scheduling data into themanufacturing execution system and to present all data records beingrelevant for the user when scheduling the production process in order tohave the user's production order scheduled and executed accordingly; d)a production scheduler database configured to store all productionorders and/or production scheduling data and to provide predefined datastored in the database to the man machine interface and/or graphicaluser interface for the user in charge of scheduling; wherein thepredefined data are determined sensitive data and/or sensitive class ofdata out of the data stored in the database, the sensitive data and/orsensitive class of data being required for a real-time scheduling; e) adata server process configured to update the sensitive data and/orsensitive class of data for the users when a user modifies at least partof the sensitive data and/or sensitive class of data; wherein said dataserver process is enabled to execute an event list queue formed of thedata modification events launched by the database, and said data serverprocess is further configured to: i) periodically check the event listqueue for data modification events covering the sensitive data and/orsensitive class of data, ii) read from the database only the modifieddata of the sensitive data and/or the sensitive class of data, and iii)merge the modified data with the existing data wherein the updated dataare accessible by all users.
 2. The system according to claim 1, whereina period for checking the event list queue is user-definable.
 3. Amethod for controlling the operations of a manufacturing facility, themethod which comprises: a) providing a plurality of production resourcesthat execute a production process according to a production schedule; b)providing a manufacturing execution system comprised of, at engineeringlevel, a production modeler for modeling the production resources andtheir production dependencies and/or constraints and a productionscheduler for scheduling the production process according to productionorders to be executed thereby using the data model of the productionmodeler; c) providing at least one man machine interface and/orgraphical user interface enabling a user to enter production ordersand/or production scheduling data into the manufacturing executionsystem and to display data that are relevant for the user whenscheduling the production process in order to have the user's productionorder scheduled and executed accordingly; d) providing a productionscheduler database for storing therein all production orders and/orproduction scheduling data and for providing predefined data stored inthe database to the man machine interface and/or graphical userinterface for the user in charge of scheduling; wherein the predefineddata are determined sensitive data and/or sensitive class of data out ofthe data stored in the database, and wherein the sensitive data and/orsensitive class of data are required for a real-time scheduling; e)providing a data server process that updates the sensitive data and/orsensitive class of data for the users when a user modifies at least partof the sensitive data and/or sensitive class of data, the data serverprocess being enabled to execute an event list queue containing the datamodification events launched by the database, and the data serverprocess being further enabled to: i) periodically check the event listqueue for data modification events covering the sensitive data and/orsensitive class of data; ii) read from the database only the modifieddata of the sensitive data and/or the sensitive class of data; and iii)merge the modified data with the existing data to generate updated dataaccessible by all users.
 4. The method according to claim 3, wherein theperiod for checking the event list queue is user-defined.